Polyacetal resins are widely used, for example, as a component of automobile parts, electronic and electrical parts, and working parts or exterior parts of other industrial apparatuses because of their excellent mechanical strength, creep characteristics, lubrication characteristics, and electric characteristics. However, when polyacetal resins are used as a component in bracketing materials for in-tank type fuel pump apparatuses as disclosed, for example, in JP-A-8-279373, the resin is simultaneously required to have the properties of electrical conductivity for the inhibition of static electricity formation caused by contact with fuel, high mechanical strength for operation at high pump pressure, and excellent releasability for smooth releasing from molds of complicated shapes produced by injection molding.
The following prior art teaches polyacetal resins having improved electrical conductivity characteristics. JP-A-63-210162 discloses a composition comprising a polyoxymethylene resin, a specific carbon black, and an epoxy compound, but this composition only has improved antistatic properties, not improved mechanical properties.
JP-A-49-37946 discloses compositions comprising a polyacetal resin containing a carbonaceous carbon fiber, and mentions, in the examples, that the fiber length of the carbon fiber in the injection molded products is in the range of 0.10-0.20 mm, and the electrical conductivity improves as the amount of the carbon fiber contained therein increases. It further discloses that mechanical strength, elastic modulus and frictional characteristics of the compositions are equal to or higher than those of polyacetal. However, the compositions have high anisotropy, and when they are injection molded (especially when they are molded into relatively large articles such as brackets of in-tank type fuel pump apparatuses). They show non-uniform shrinking behavior in the mold resulting in clamping of the mold and deterioration of releasability from the mold.
JP-A-62-267351 discloses a polyacetal resin composition containing one or two or more of carbon materials selected from the group consisting of carbon black, carbon fiber and graphite in an amount of 0.1-30% by weight based on the whole composition and one or two or more compounds selected from the group consisting of alkali metal compounds and alkaline earth metal compounds in an amount of 0.0005-2% by weight based on the whole composition. The publication states that the heat stability of the polyacetal resin containing the carbon materials is improved by the addition of the alkali metal compounds and/or the alkaline earth metal compounds, but makes no mention of the examples where they are used in combination, and fails to disclose excellent effects in all of the electrical conductivity, the mechanical properties and the releasability as attained in the present invention.
JP-A-6-240049 discloses a thermoplastic resin composition comprising a carbon fiber of 1-6 .mu.m in diameter contained in an amount of 3-30 wt % in the thermoplastic resin and carbon black contained in an amount of 0-20 wt % in the thermoplastic resin. As the thermoplastic resin, a polyoxymethylene resin is mentioned, and examples including it are given, but all of the examples use only carbon fiber as the carbon material. Thus, naturally, the effects obtained in the present invention are not shown.